VOIP over MPLS network with bandwidth util of 50%

Unanswered Question
Aug 8th, 2007

We are in the process of upgrading our bandwidth at our branch locations into 3 Mbps MPLS networ and we only run Citrix traffic and IP Voice (Interoffice calls) from our Branch locations into our HQ.

We expect Bandwith utilization to typically max out at 1.6 MBPS. Do you think we need to configure QoS for the voice traffic since the circuit will only be 40-50 percent utilized? My thinking was why should I configure QoS if the bandwidth is only at 40 - 50 percent. The voice traffic should have enough bandwidth to communicate over the wire.

Is my thinking correct or should I configure QoS across this MPLS network?

Any responses are greatly appreciated

I have this problem too.
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PETER NEGUS Wed, 08/08/2007 - 06:30

You really do need your QoS. Two reasons:

(a) Your average 40-50 % contains peaks of near 100%, which may result in packet drops. On a compressed voice call, even 1% is enough to severely degrade quality.

(b) Your average will conceal peaks and troughs of traffic queues. At the peaks, average queue lengths will increase, creating jitter (variation in arrival time of voice packets). More than 50ms of jitter, and your voice session is trashed.

mdargin Wed, 08/08/2007 - 06:37

I am confused when you say peaks of near 100%. When I measure bandwith using solarwinds I see the peaks reach 50%. Solarwinds captures in 1 minute intervals.

PETER NEGUS Wed, 08/08/2007 - 07:02

1 minute is a lifetime in Voip. The VoIP sampling interval is typically 20ms, so if you see 100% for over 100ms it is goodbye vienna.


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